Electrical resistor and its manufacture



Nov. 26, 1935.

A. H. HEYROTH ET AL ELECTRICAL RESISTOR AND ITS MANUFACTURE Filed Dec.29, 1953 IN VENTORS.

ATTORNEY.

Patented Nov. 26, 1935 UNITED STATES PATENT OFFICE ELECTRICAL RESISTORAND ITS MANUFACTURE I New York Application December 29, 1933, Serial No.704,584

4 Claim.

This invention relates to electrical resistors, more particularly toresistors intended for use as heating elements and radiators, and tomethods of making the same.

Electrical resistors for use in radiating heat are ordinarily made bywrapping wire composed of refractory metal on refractory supports. Verysatisfactory non-metallic radiators are made in the form of rodscomposed mainly of silicon carbide. These rods require support only attheir ends. Both the metal wire resistors and the resistor rods areordinarily operated at temperatures in excess of 500-600 C.; that is, attemperatures which produce a dull red to a bright red tint in theresistor.

One of the objects of our invention is to provide an electrical resistorfor use at temperatures extending up to a dull red heat and in which theheat is distributed from a comparatively large area. Another object ofour invention is to produce a resistor at low cost by simplification ofthe methods of manufacture.

The invention is illustrated by means of the accompanying drawing inwhich:

Figure 1 is a side view of a resistor made according to our invention;

Figure 2 is a section taken on the line 11-11 of Figure 1;

Figure 3 is a section taken on the line IIIIII of Figure 1;

Figure 4 is a side view of a resistor which is similar to that shown inFigure 1 except in the mounting or support for the resistor, a strip ofceramic material being substituted for the tube;

Figure 5 is a section on the line V-V of Figure 4;

Figure 6 is a side view of a U-shaped resistor which is mounted on aceramic support; and

Figure 7 is a section on the line VII-VII of Figure 6.

Referring to the drawing in detail, 2 represents an insulating tube ofrefractory material such as is used, for example, in clay insulators. Onthe outside of this tube is a conducting coating composed principally ofsilicon and a form of clay known as bentonite. This is a. clay-likematerial which has a large power of absorption of water and which iseasily fusible after drying. On the terminal portions of the conductingcoating are layers 4 of highly conducting metal. These may be produced,for example, by electroplating copper on the terminal portions of theresistor or by spraying brass or other conducting metal which is easilysprayed. The spraying can be performed with a Schoop gun.

As an illustration of a method of making our improved resistor, anunglazed clay tube or ceramic body of the shape and dimensions desiredfor heat distribution is selected. Metallic silicon is ground to about200 mesh (meshes to the linear inch). About 84 parts of this finelydivided silicon are mixed with 16 parts of bentonite, and the mixture ofsilicon and bentonite is dispersed in about twice the mass of water withthe aid of an agitator until a slurry suitable for application to theunglazed clay tube (or other form of ceramic body) is formed. The slurrymay be applied by dipping the ceramic body in the dispersion or theslurry may be painted on the surface of the tube. After the firstcoating has dried, a. second coating can be applied and the processrepeated a number of times depending on the degree of conductance whichit is desired to obtain in the finished product. The coated tube is thenplaced, for example, in a muffle and fired at a temperature of about2300" F. The silicon will remain substantially unaltered even in anoxidizing atmosphere if not heated too long at the temperaturementioned. About twenty minutes firing is needed for a tube six incheslong and five eighths of an inch in diameter. The resultant coating hasa hard, smooth surface which is not easily scratched. Terminals of high-1y conducting metal are provided by electroplat- 3o distributed from asubstantially plane surface which is heated more uniformly than ispossible with the use of a wire grid, for example.

In the modification shown in Figures 6 and 7, a strip of ceramicallybonded refractory is covered with a U-shaped resistor layer 8. The endsof the resistor layer are provided with terminal connections 9 and 9' atthe respective ends by depositing or spraying highly conducting metal onthe terminal portions of the resistor layer. The coating at the U-shapedbend ll may be made narrower or thinner than the remainder of theresistor coating so that this area becomes red hot while the remainderof the resistor is cooler. This affords a convenient method oflocalizing heat on an outstanding area.

Our resistor has a number oi advantages. both from the manufacturingpoint oi view and an an electrical resistor.

ing and described above as an electrical resistor,

some or the advantages are:

Low cost of replacement;

* the oi metal wire heater temperature are distributed Z and nil-lg, Theresistor can be wiped and the like without injury to resistor.

:se of distribution oi radiant iesiritcr, it: is mounted, ior mu 3;position that its longitudinal i el coincides with the focal axle t winga principal section. which ril- UCLUtheaiahandterminalmetaletrlpeattachedto the sides 0! the U-shapedcoating.

2. The method of making an electric heater which comprises making aslurry of approximate- 1y five parts of finely divided silicon and onepart 0! nnely divided bentonite in a mass or water which is greater thanthat of the tinely divided solids, applying the slurry to the twooppoaite sides of a refractory slab which is an electrical insulator andapplying also a thinner coating of the slurry to the curved suriacewhich joins the said opposite sides, baking the coating on the mountingat a. temperature exceeding 2000 Fahrenheit, and spraying highlyconducting metal on the opposite sides of the U-shaped resistor thusformed.

3. An electric heater comprising a refractory base in the term ci anon-conducting 'slab having a rounded end, a conducting layer composedof silicon and a seli-fluxing binder baked metal strips attached to thesides oi the U-shaped coating.

4. The method 01' making an electric heater 1 which comprises making aslurry of finely divided silicon and a smaller proportion or selffiuxing binder in a mass 01 water which is great-- or than that of thefinely divided solids, applying the slurry to the two opposite sides ofa reiractory slab which is an electrical insulator, and applying also athinner coating of the slurry to the curved surface which joins the saidopposite sides, baking the coating on the mounting at a temperatureexceeding 2000 Fahrenheit, and

spraying highly conducting metal on the opposite sides of the U-shapedresistor thus formed.

ALBERT H. HEYROTH. WALTER E. SCHHDHAUER,

